The purpose of the proposed research is to systematically examine the behavioral capacity for stereoscopic vision in two predatory vertebrates, the cat and the falcon. The binocular visual system of the cat resembles that of primates, and extensive neurophysiological research suggests a neural basis for stereopsis in the cat. Only recently has a behavioral demonstration of stereoscopic vision in the cat been made. Further research is required to specify the quality and accuracy of stereopsis in the cat so that behavioral data can be used to evaluate hypotheses derived from the neurophysiological inquiry. Because the binocular visual system of nonmammalian predators such as the falcon is organized so differently from mammalian systems, it is uncertain whether stereopsis is a special property of mammals or whether it is a general characteristic of predatory vertebrates. The outcome of behavioral tests of stereopsis in the falcon will help to resolve that question and will serve to specify the scope of subsequent neurophysiological investigation.